Aneurysm of descending thoracic aorta, in majority of cases is diagnosed either by chance in routine chest imaging for some other reasons or rarely due to it's symptomatic presentation like chest pain and other mediastinal compression symptoms. In this case report we present a case of 69 year old smoker who presented with cough, hemoptysis and left sided massive painless hemorrhagic pleural effusion. Further investigation revealed a large aneurysm of descending thoracic aorta which infiltrated the left lung. We suggest descending thoracic aneurysm be included in the differential diagnosis of this sort of clinical presentation which otherwise imperative with the clinical scenario of bronchogenic carcinoma.